A new method for the selective quantitation of cyanogenic glycosides by membrane introduction mass spectrometry

A new method is described for the rapid, sensitive, virtually interference-free, and selective quantitation of cyanogenic glycosides in aqueous extracts using membrane introduction mass spectrometry (MIMS). Selective monitoring, by either conventional MIMS or cryotrap-MIMS, not of HCN but of the co-released ketones (acetone and butan-2-one), when performed for both the crude cassava extracts and the linamarase-NaOH-hydrolyzed extracts, is found to offer an advantageous alternative to classic spectrophotometric methods based on HCN analysis for the selective quantitation of the two cyanogenic glycosides linamarin and lotaustralin expressed as both the free HCN content and the total cyanogenic potential (total HCN).12591529153

Dehydrobenzoyl cations: Distonic ions with dual free radical and acylium ion reactivity

In the gas phase, m- and p-dehydrobenzoyl cations display strong duality of chemical behavior. The ions react selectively as either free radicals or acylium ions, depending on the choice of the neutral reaction partner. Transacetalization with 2-methyl-1,3-dioxolane, ketalization with 2-methoxyethanol, and epoxide ring expansion with epichlorohydrin demonstrate their acylium ion reactivity, whereas (SCH3)-S-. abstraction with dimethyl disulfide demonstrates their free radical reactivity. In one-pot reactions with gaseous mixtures of epichlorohydrin and dimethyl disulfide, the m- and p-dehydrobenzoyl cations react selectively at either site to form the two monoderivatized ions in variable but controlled yields; further reaction at either the remaining radical or the acylium charge site forms a single biderivatized ion as the final product. The o-dehydrobenzoyl cation also displays the expected radical and acylium ion reactivities. But for the ortho isomer, binding of the nucleophilic neutral to the free or derivatized C+=O group facilitates reactions at the radical site. Hence, the ortho isomer displays a unique behavior; its acylium ion reactions either occur simultaneously with, or are followed by, H-abstraction radical reactions. As shown by ab initio calculations, the three isomers display sigma-localized odd-spin and pi-delocalized charge densities, which characterize distonic structures with molecular orbital-separated radical and charge sites. The dehydrobenzoyl cations are also, according to the calculations, the most stable among 19 of the most feasible C7H4O+. isomers.12043111361114

Acyclic distonic acylium ions: Dual free radical and acylium ion reactivity in a single molecule

Three gaseous acyclic distonic acylium ions: . CH2-CH2-C+=O, . CH2-CH2-CH2-C+=O, and . CH2=C(CH2)-C+=O, are found to display dual free radical and acylium ion reactivity; with appropriate neutrals, they react selectively either as free radicals with inert charge sites, or (and more pronouncedly) as acylium ions with inert radical sites. The free radical reactivity of the ions is demonstrated via the Kenttamaa reaction: CH3S. abstraction with the spin trap dimethyl disulfide; their ion reactivity by two reactions most characteristic of acylium ions: transacetalization with 2-methyl-1,3-dioxolane and the gas-phase Meerwein reaction, that is, expansion of the three-membered epoxide ring of epichlorohydrin to the five-membered 19-dioxolanylium ion ring. In "one-pot" reactions with gaseous mixtures of epichlorohydrin and dimethyl disulfide, the ions react selectively at either site, bur more readily at the acylium charge site, to form the two mono-derivatized ions. Further reaction at either the remaining free radical or acylium charge site forms a single bi-derivatized ion as the final product. Becke3LYP/6-31G(d) calculations predict the reactions at the acylium charge sites of the three distonic ions to be highly exothermic, and both the "hot" transacetalization and epoxide ring expansion products of . CH2-CH2-CH2-C+=O to dissociate rapidly by H2C=CH2 loss in overall exothermic processes. The calculations also predict highly spatially separate odd spin and charge sites for the novel cyclic distonic ketal ions formed by the reactions at the acylium charge sites. (J Am Soc Mass Spectrom 2000, 11, 697-704) (C) 2000 American Society for Mass Spectrometry.11869770

Structurally diagnostic ion-molecule reactions: acylium ions with alpha-, beta- and gamma-hydroxy ketones

Gas-phase reactions of four acylium ions and a thioacylium ion with three isomeric alpha-, beta- and gamma-hydroxy ketones are performed by pentaquadrupole mass spectrometric experiments. Novel structurally diagnostic reactions are observed, and found to correlate directly with interfunctional group separation. All five ions tested (CH(3)CO(+), CH(2)=CHCO(+), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+)) react with the gamma-hydroxy ketone (5-hydroxy-2-pentanone) to form nearly exclusively a cyclic oxonium ion of m/z 85 that formally arises from hydroxy anion abstraction. With the beta-hydroxy ketone (4-hydroxy-2-pentanone), CH(2) = CHCO(+), PhCO(+) and (CH(3))(2)NCO(+) form adducts that undergo fast cyclization via intramolecular water displacement, yielding resonance-stabilized cyclic dioxinylium ions. With the alpha-hydroxy ketone (3-hydroxy-3-methyl-2-butanone), PhCO(+), (CH(3))(2)NCO(+) and (CH(3))(2)NCS(+) form stable adducts. Evidence that these adducts display cyclic structures is provided by the triple-stage mass spectra of the (CH(3))(2)NCS(+) adduct; it dissociates to (CH(3))(2)NCO(+) via a characteristic reaction-dissociation pathway that promotes sulfur-by-oxygen replacement. If cyclizations are assumed to occur with intramolecular anchimeric assistance, relationships between structure and reactivity are easily recognized. Copyright (C) 2001 John Wiley Sons, Ltd.37216216

Transacetalization of 1,3-dioxane with acylium and sulfinyl cations in the gas phase

Transacetalization occurs extensively In gas phase ion-molecule reactions of 1,3-dioxane with a variety of acylium ions [R-C+=O; R = CH3, C2H5, Ph, CH3O, Cl, CH2=CH, (CH3)(2)N] and a sulfur analogue, the thioacetyl ion CH3-C+=S. Six-membered 1,3-dioxanylium ions and analogues, i.e. cyclic 'ionic (thio)ketals', are formed, as evidenced by pentaquadrupole triple-stage collision-dissociation mass spectra and MP2/6-311G(d,p)//6-311G(d,p) + ZPE ab initio calculations, as well as by O-18 labelling experiments. Transacetalization with 1,3-dioxane is not a general reaction for sulfinyl cations (R-S+=O). They react either moderately (CH3-S+=O) or extensively (CH2=CH-S+=O) by transacetalization, form abundant intact adducts (Ph-S+=O) or undergo mainly proton transfer and/or hydride abstraction reactions (Cl-S+=O, CH3O-S+=O and C2H5O-S+=O). Competitive MS2 experiments are employed to compare the transacetalization reactivity of different acylium ions, and that of two cyclic neutral acetals, that is 1,3-dioxane and 1,3-dioxolane. All the cyclic 'ionic ketals) dissociate exclusively under low-energy collision conditions to regenerate the original reactant ion species, a simple dissociation chemistry that is amply demonstrated to be a very general characteristic of the transacetalization products. The cyclic 'ionic thioketal' formed in transacetalization with CH3-C+=S is found, however, to dissociate exclusively to the oxygen analogue ion CH3-C+=O, a triple-stage mass spectrometric(MS3) experiment that constitutes a novel gas-phase strategy for conversion of thioacylium ions into acylium ions.102105211

The gas-phase Meerwein reaction

A systematic investigation of a novel epoxide and thioepoxide ring expansion reaction promoted by gaseous acylium and thioacylium ions is reported. As ab initio calculations predict, and O-18-labeling and MS3 pentaquadrupole experiments demonstrate, the reaction proceeds by initial O(S)-acylation of the (thio)epoxides followed by rapid intramolecular nucleophilic attack that results in three-to-five-membered ring expansion, and forms cyclic 1,3-dioxolanylium, 1,3-oxathiolanylium, or 1,3-dithiolanylium ions. This gas-phase reaction is analogous to a condensed-phase reaction long since described by H. Meerwein (Chem. Ber. 1955, 67, 374), and is termed as "the gas-phase Meerwein reaction"; it occurs often to great extents or even exclusively, but in some cases, particularly for the most basic (thio)epoxides and the most acidic (thio)acylium ions, proton transfer (eventually hydride abstraction) competes efficiently, or even dominates. When (thio)epoxides react with (thio)acylium ions, the reaction promotes O(S)-scrambling; when epoxides react with thioacylium ions and the adducts are dissociated, it promotes S/O replacement. An analogous four-to-six-membered ring expansion also occurs predominantly in reactions of trimethylene oxide with acylium and thioacylium ions.6589790

Ketalization of gaseous acylium ions

A novel reaction of gaseous acylium ions: ketalization with diols and analogs, has been systematically studied via pentaquadrupole MS2 and MS3 experiments and ab initio calculations. A variety of alpha,beta -diols and their amino, thiol, ether, and thioether analogs have been tested for reactivity, mechanism evaluation, site selectivity, and for the effects of alpha- and beta -interfunctional separation. As for condensed-phase ketalization of neutral carbonyl compounds followed by hydrolysis, gaseous acylium ions are chemically deactivated in the form of cyclic ionic ketals by ketalization, and are efficiently released via on-line collision-induced dissociation. Ketalization of acylium ions is shown to identify and structurally characterize alpha,beta -diols and their analogs, and to distinguish regioisomers. Diastereomers can also be distinguished, as illustrated for cis and trans 1,2-diaminocyclohexane. The MS2 and MS3 data together with O-18-labeling and ab initio calculations establish for acylium ion ketalization a mechanism of anchimeric assistance with participation of the neighboring acyl group. (C) 2001 American Society for Mass Spectrometry.12215016